Electrodeposition of iron-zinc alloys



Uni sd St s awfl r ELECTRODEPUSITKGN F IRON-ZINC ALLOYS William H.Safranelr, Columbus, Ohio, assignor, by mesne assignments, to RockwellSpring and Axle Company, Coraopolis, Pm, a corporation of PennsylvaniaNo Drawing. Application August 2, 1954 Serial No. 447,402

6 Claims. (Cl. 204-43) This invention relates to electroplating. Moreparticularly, it relates to an iron-alloy electrodeposit.

In the plating of steel parts with chromium, it is necessary to polishand then buff the surface of the steel before applying the chromiumcoating. Frequently,'a layer of nickel is electroplated on the steel,and the nickel is then buffed before the final plating with chromium.The bufiing operations are costly steps because large quantities ofbuffing materials are consumed, and much time is required to performthis operation.

Alternatively, a layer of copper is plated on the polished steel usingspecial baths which produce fine-grained, leveling-type plates. A layerof nickel is then plated on the copper. The superpositioning of thefine-grained copper undercoat improves the buifability of the nickelplate, with the result that bufling costs are markedly reduced. However,the copper-plating step is nearly as costly as the savings made in thebufiing operation. Also, special addition agents and equipment arerequired.

It has now been found that by the method and bath of this invention, aductile and leveling-type iron-alloy plate can be electrodeposited. Thisiron-zinc-alloy electrodeposit fills in polishing scratches and otherirregularities in the surface of the basis metal so that the platedsurface is smoother than the original basis metal surface. This levelingiron-alloy plate can be overplated with bright nickel plate, such as theductile and leveling nickel.

plate disclosed in copending applications Serial Nos. 368,903, filedJuly 20, 1953; 369,223, now abandoned, filed July 20, 1953, and 369,224,now Patent No. 2,748,-

068, filed July 20, 1953. The combination of a leveling A iron alloy andnickel plate completely obviates the necessity of a buffing step, sincethe plating operations provide an attractive final appearance, even whenthe polished steel surface had a roughness before plating, of 20 R. M.S. microinches or more.

Should a dull or semibright nickel be used in place of bright nickelplating, the deposition of the iron-zinc alloy prior to the nickelplating greatly improves the butfability of the dull nickel plate.

Accordingly, one of the objects of this invention is to provide aductile iron-alloy coating.

Another object is to provide economical means for smoothing polishedsteel surfaces prior to plating with chromium or nickel and chromium.

A further object is to improve the corrosion protection afforded by ironelectroplates by codepositing zinc or zinc and nickel with the iron.

Other objects and advantageous features will be apparent from thefollowing detailed description.

In general, this invention relates to electrodepositing an iron-zincalloy from an aqueous bath comprising ferrous ions and zinc ions. Theelectroplate produced by this process contains from 2 to percent zinc,and the balance iron, and is both leveling and ductile. The plate mayalso contain from 3 to 16 percent nickel replacing a part of the iron.

The ferrous ions are introduced into the bath by means of iron powder orsoluble ferrous salts such as ferrous sulfate, ferrous ammonium sulfate,or ferrous sulfamate. The ferrous iron concentration can vary from 20 to100 g./l. about 35 and g./l. is preferred for best leveling andductility.

Oxidation by air or some other oxidizing agent may cause the ferrousiron to be oxidized to ferric iron. However, the ferric ironconcentration should not exceed 0.3 g./l. The build-up of the ferriciron concentration may be avoided by using a large iron anode area. Itmay also be desirable to immerse in the bath iron rods which are notconnected to the anodes.- Ferric iron in' the bath will be substantiallyreduced to ferrous iron by reaction with these iron rods. Iron or zincpowder may also be introduced into the bath for this purpose.

The zinc may be added to the bath either in the form of zinc powder, oras a soluble zinc salt, such as zinc sulfate. The concentration of zincin the bath depends upon the iron concentration; the ratio of zinc toiron is between 0.004 and 0.05 to l for depositing the ductile,

leveling iron alloy containing 2 to 15 percent zinc. Thus, in a bathcontaining 50 g.,/l. ferrous iron, the zinc concentration is between0.25 and 2.5 g./l.

In addition to iron and zinc, other metals may be added to the bath forimproving the physical properties of the plate, or its corrosionresistance. For example, the addition of nickel to the bath in the formof nickel sulfate, nickel ammonium sulfate, or nickel sulfamate inamount to give a nickel-iron ratio of between 0.05 and 1.25 to 1, willresult in iron-rich alloy plate containing, in addition to the zinc,about 3 to 16 percent nickel, which, in combination with the zincassists in improving the ductility, the leveling action, and thecorrosion resistance of the iron-alloy plate.

The pH of the bath is preferably adjusted to between 1.5 and 3.5 byadding sulfuric acid to reduce the pH or ammonium hydroxide to raise it,as required. The bath may be operated outside this range for shortperiods of time, but operating at a pH greater than about 3.5 willcauseprecipitation of the ferrous iron.

The temperature of the bath should be maintained at between aboutv and220 F. for satisfactory plating. For best leveling and ductility, atemperature range of from to F. is preferred.

. Suitable anodes for electrodepositing the alloy of this inventioninclude iron rods containing very low carbon or low-carbon steel sheet,such as SAE 1010 or SAE 1020. Iron anodes may be used continuously forlong operating periods without the necessity of cleaning or otherwisetreating them. If steel anodes are used, it may be necessary toperiodically remove carbon sludge formed on the surface of the anodeduring continuous operation. Best results are obtained by bagging theanodes with a material such as cotton duck.

It may be desirable to add to the plating bath a buffer, such as boricacid or ammonium sulfate. A wetting agent may also be used to preventpitting in the deposits. Suitable wetting agents include sulfatedoxyalcohols, such as the product made by reacting coconut alcohol withethylene oxide, followed by sulfating with sulfuric acid.

Sulfated alcohols, such as sodium lauryl sulfatemay also I be used.

vention with greater particularity:

Example I vA 0.001-inch alloy plate containing about 5 percent.

Patented Apr. 29, 1958 3 However, a ferrous iron concentration between.

sesame Ferrous sulfate [FeSO -6H Ol g./-l 300.0 Boric acid [H 50 g./l30.0 Sulfated oxyalcohol g./l 0.5 Zinc sulfate [ZnSo -7H Ol g./l 1.8Water Balance pH 2.3 Temperature F.. 135:3 Cathode current density amp./sq. ft 50 Anode current density amp./sq. ft" 25 Plating time min 30 Theworkpiece was agitated by moving it in the bath 30 cycles per minuteusing a 1-inch stroke.

The anodes were SAE 1010 steel plate, about Aa-iuch thick, covered withcotton duck bags. The iron consumed by plating was replenished by theanodes. The zinc codeposited with the iron was replenished by addingzinc powder at the rate of about 3.5. grams per 100 ampere hours ofoperation. Each time zinc powder was dis solved, a small quantity ofsulfuric. acid was added to keep the pH of the bath in the range of 2.1to 2.4.

The resulting electroplate had a roughness of from 11 to 13 R. M- S.rnicroinches when deposited over polished steel having a roughness offrom 13 to 16 R. M. S. microinches, or an average leveling of percent.

Example II A bath was operated similar to that of Example 1, except thatthe zinc sulfate concentration was 6.2 g./l., the pH was 2.5, and thetemperature was l60- -3 F.

The resulting 0.001-inch electroplate contained about 12 percent zinc,and had a roughness of from 14 to 17 R. M. S. microinches, when platedover polished steel having a roughness of from 19 to 23 R. M. S.microinches. The average reduction in roughness was 25 percent.

Example III A 0.00l-inch alloy plate containing about 2 percent zinc andthe balance iron was electrodeposited on steel using the following bathand operating conditions.

Ferrous sulfamate [Fe(SO NH g./l 160.0 Boric acid [H BO l g./l 30.0 Zincsulfate [ZnSO -7H O] g./l 0.9 Water Balance pH 1.9 Temperature F 145Cathode current density amp./sq. ft 50 Anode current density amp./sq. ft25 Plating time min The workpiece was agitated by moving it in the bath30 cycles per minute, using a 1-inch stroke.

The resulting electroplate had a roughness of from 9 to 12 R. M. S.microinches over a polished steel plate having a roughness of from 18 to20 R. M. S. microinches, or an average leveling of percent.

Example IV Example V A very good leveling and corrosion-resistant platewas produced containing 1.5 percent Zinc, 16 percent nickel,

"r; and the balance iron. The bath used had the following composition:

Ferrous sulfate [FeSO -7H Ol g./l 300.0 Boric acid [H ....g./l.... 30.0Nickel sulfate [NiSO -7H O] g./l 350.0 Sulfated oxyalcohol g./l 0.5 Zincdust g./l 0.25 Water Balance pH 2.2 Temperature F l30 Cathode currentdensity amp./sq. ft 50 A comparable bath, omitting the zinc, producedplates which were highly stressed and were cracked, especially near theedges. The zinc addition reduced the stress and eliminated the cracking.

The electrodeposition of zinc with iron also resulted in a more ductileplate. Iron was plated on a fii-inch steel panel, and the plated panelwas bent around a l/z-inch diameter arbor. A bend of only five degreescaused severe cracking in the iron plate.

Similar steel panels plated with the iron-zinc alloy of this inventioncould be bent at least 25 degrees and usually as much as 45 degreesbefore the first appearance of microscopic cracks. Even after a bend ofdegrees, the cracking of the iron-zinc alloy plating was less severethan that resulting from bending the iron plating only five degrees. 7

A nickel plate deposited directly on the 0.00l-inch iron-zinc depositswas much easier to bufi. to desired brightness than nickel plateddirectly on polished steel. Also, a decorative chromium plate(0.0000l-inch) had superior corrosion resistance when plated over thenickel, iron-zinc, polished steel combination than when plated over anickel and polished steel alone. The following table shows the resultsof salt spray-fogtest:

In summary, there has been disclosed a novel bath and process forelectrodepositing an iron-alloy plate. The alloy plating produced bythis process contains from 2 to 15 percent zinc, and the balance iron,and is a ductile and leveling plate. Additionally, the plate may containfrom 3' to 16 percent nickel. Although specific examples have been givento illustrate this invention, it is not intended to be limited thereby,but only by the scope of the specification and claims.

What is claimed is:

1. The process of electrodepositing a leveling, ductile, iron-zinc-alloyplate which comprises electrolyzing an aqueous acid solution containinga ferrous compound with ferrous ion in a concentration of 20 to g./l.,and a zinc compound with zinc ion in a zinc-ferrous ratio of from 0.004to 0.05.

2. The method according to claim 1 wherein the temperature of thesolution is from 100 to 220 F.

3. The method according to claim 1 wherein the pH is from 1.5 to 3.5.

4. The process of clectrodepositing a leveling, ductile,iron-zinc-nickel-alloy plate which comprises electrolyzing an aqueousacid solution containing a ferrous compound with ferrous ion in aconcentration of 20 to 100 g./l., a zinc compound with zinc ion in azinc-ferrous ratio of from 0.004 to 0.05, and a nickel compound withnickel ion in a nickel-ferrous ratio of from 0.05 to 1.25.

5. A composition of matter useful in the deposition of iron-zinc-alloyelectroplates which comprises an aqueous solution of a ferrous compoundof from 20 to 100 g./l. References Cited in the file of this patentferrous ion and a zinc compound with zinc ion in a zinc- UNITED STATESPATENTS ferrous ratio of from 0.004 to 0.05.

6. A composition of matter useful in the deposition 6502 Babcock June1849 of iron-zinc-nickel-alloy electrodeposit which comprises 5 8114Boyden May 1851 an aqueous solution containing a ferrous compound with1,072,091 cowper'coles Sept 1913 ferrous ion in a concentration of 20 to100 g./l., a zinc 1,791,642 Schulte 1931 compound with zinc ion in azinc-ferrous ratio of from 2,418,970 Domoe 1947 0.004 to 0.05, and anickel compound with nickel ion in a nickel-ferrous ratio of from 0.05to 1.25. 10

1. THE PROCESS OF ELECTRODEPOSING A LEVELING, DUCTILE, IRON-ZINC-ALLOYPLATE WHICH COMPRISES ELECTROLYZING AN AQUEOUS ACID SOLUTION CONTAININGA FERROUS COMPOUND WITH FERROUS ION IN A CONCENTRATION OF 20 TO 100G./L., AND A ZINC COMPOUND WITH ZINC ION IN A ZINC-FERROUS RATIO OF FROM0.004 TO 0.05.